Devices of the predated type serve to convert a rotary motion into a translational motion. They are suitable for use in fields where only a limited stroke of the threaded spindle is required e.g., in an actuator of an electromechanical brake or in an electrically operated parking brake of a vehicle.
In such a device known from the published application DE 197 05 106 A1, two ball screw drives are combined with each other, namely, an inner screw drive made up of the spindle, the nut and inner rolling elements, and an outer screw drive made up of the nut, an additional nut surrounding this nut and outer rolling elements. By the cooperation of the two screw drives a desired, small total pitch is obtained as the difference between the individual pitches of the two screw drives. This enables the use of standard threads to achieve a very small resultant pitch of the brake device. Such a combination of ball screw drives, however, has the drawback of an expensive structural configuration and increased design space requirement.